1. Field of the Invention
The present invention relates to water absorption test for an insulator of a stator winding of a power generator, and more particularly, to a water absorption testing apparatus of an insulator of a stator winding of a power generator using a cross capacitance in which a deteriorated winding is detected by determining whether or not the insulator of the stator winding of a power generator absorbs cooling water according to thickness using the cross capacitance such that a power station is prevented from being suddenly stopped, costs for the maintenance are reduced, and the lifespan of the power generator is extended.
2. Description of the Related Art
Generally, a high capacity power generator is a water cooling type generator, and heat generated while making electricity is cooled by water. Particularly, for the cooling of a stator winding of the generator, pure water having a high efficiency is used.
However, when an insulator of the stator winding of the generator absorbs moisture or water, insulation is broken during the operation of the generator thereby causing accident of the unwanted generator trip. Thus, the operation reliability of the generator is deteriorated, costs and time for replacing the winding with new one are increased so that the productivity of generating electricity is deteriorated.
As a conventional method of water absorption test for generator stator winding insulator, there is a tan δ test and a method of measuring general capacitance between two plates for the diagnosis.
Here, the tan δ is a dielectric tangent, while the dielectric tangent (tan δ) is a tan function of a phase difference (δ) of a dielectric substance between perfect capacitive current and measured current. Since an ideal dielectric substance has only capacitance components, δ may be 90 degrees. Thus, the tan δ may be infinite value. However, when the dielectric substance is inferior, resistance component is generated so that δ is less than 90 degrees. The dielectric tangent test uses the point that a loss is generated when an AC voltage is applied to the insulator. This loss is divided into a loss due to a leak current, a loss due to dielectric polarization, and a loss due to partial discharge. Because of these losses, overall current is delayed more than a charged current component, while this delayed angle is known as a dielectric loss angle, and the tangent thereof is known as the dielectric tangent. When an applied voltage is known, the capacitance can be known, and when the loss angle is known, the loss can be known.
However, the tan δ can determine whether or not the insulation of the phase of the winding is good, but cannot determine whether or not the water absorption has occurred in respective windings.
Moreover, in the method of measuring the general capacitance between two plates for the diagnosis, the water absorption of the insulator of the winding can be determined. However, an error with respect to variation of thickness of the winding insulator is likely to be generated in the testing apparatus during the water diagnosis. Additionally, since stray capacitance generated during the measurement cannot be removed, there is no solution of avoiding the error.
Moreover, there is no measuring information of the tan δ with respect to the respective windings, and the water absorption of the insulator of the stator winding of the generator cannot be measured in relation to the thickness.
Therefore, in order to solve the above technical problem, in the present invention, a water absorption testing apparatus is developed by applying a cross capacitance theory to the water absorption test of the insulator of the stator winding of a generator.